diff --git a/layout/style/CSSStyleSheet.cpp b/layout/style/CSSStyleSheet.cpp
index 6c79946753c9..ea1878949e52 100644
--- a/layout/style/CSSStyleSheet.cpp
+++ b/layout/style/CSSStyleSheet.cpp
@@ -601,8 +601,8 @@ CSSStyleSheet::List(FILE* out, int32_t aIndent) const
 }
 #endif
 
-void 
-CSSStyleSheet::ClearRuleCascadesInternal()
+void
+CSSStyleSheet::ClearRuleCascades()
 {
   // We might be in ClearRuleCascadesInternal because we had a modification
   // to the sheet that resulted in an nsCSSSelector being destroyed.
@@ -628,6 +628,10 @@ CSSStyleSheet::ClearRuleCascadesInternal()
       (*iter)->ClearRuleCascades();
     }
   }
+
+  if (mParent) {
+    static_cast<CSSStyleSheet*>(mParent)->ClearRuleCascades();
+  }
 }
 
 void
diff --git a/layout/style/CSSStyleSheet.h b/layout/style/CSSStyleSheet.h
index 4259862787cf..a90fea404a69 100644
--- a/layout/style/CSSStyleSheet.h
+++ b/layout/style/CSSStyleSheet.h
@@ -178,7 +178,7 @@ private:
 protected:
   virtual ~CSSStyleSheet();
 
-  void ClearRuleCascadesInternal() override;
+  void ClearRuleCascades();
 
   // Add the namespace mapping from this @namespace rule to our namespace map
   nsresult RegisterNamespaceRule(css::Rule* aRule);
diff --git a/layout/style/ServoStyleSheet.cpp b/layout/style/ServoStyleSheet.cpp
index 3ef739872519..a6b273e07bf1 100644
--- a/layout/style/ServoStyleSheet.cpp
+++ b/layout/style/ServoStyleSheet.cpp
@@ -219,15 +219,6 @@ ServoStyleSheet::Clone(StyleSheet* aCloneParent,
   return clone.forget();
 }
 
-void
-ServoStyleSheet::ClearRuleCascadesInternal()
-{
-  for (StyleSetHandle& setHandle : mStyleSets) {
-    setHandle->AsServo()->NoteStyleSheetsChanged();
-    setHandle->AsServo()->UpdateStylistIfNeeded();
-  }
-}
-
 CSSRuleList*
 ServoStyleSheet::GetCssRulesInternal(ErrorResult& aRv)
 {
diff --git a/layout/style/ServoStyleSheet.h b/layout/style/ServoStyleSheet.h
index 57aa098efd0c..fb8441d7e773 100644
--- a/layout/style/ServoStyleSheet.h
+++ b/layout/style/ServoStyleSheet.h
@@ -123,8 +123,6 @@ public:
 protected:
   virtual ~ServoStyleSheet();
 
-  void ClearRuleCascadesInternal() override;
-
   ServoStyleSheetInner* Inner() const
   {
     return static_cast<ServoStyleSheetInner*>(mInner);
diff --git a/layout/style/StyleSheet.cpp b/layout/style/StyleSheet.cpp
index 8dc4bc4ff1cd..2f94d9d3b781 100644
--- a/layout/style/StyleSheet.cpp
+++ b/layout/style/StyleSheet.cpp
@@ -127,15 +127,6 @@ StyleSheet::TraverseInner(nsCycleCollectionTraversalCallback &cb)
   }
 }
 
-void
-StyleSheet::ClearRuleCascades()
-{
-  ClearRuleCascadesInternal();
-  if (mParent) {
-    mParent->ClearRuleCascades();
-  }
-}
-
 // QueryInterface implementation for StyleSheet
 NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(StyleSheet)
   NS_WRAPPERCACHE_INTERFACE_MAP_ENTRY
@@ -448,7 +439,14 @@ StyleSheet::EnsureUniqueInner()
   mInner = clone;
 
   // Ensure we're using the new rules.
-  ClearRuleCascades();
+  //
+  // NOTE: In Servo, all kind of changes that change the set of selectors or
+  // rules we match are covered by the PresShell notifications. In Gecko that's
+  // true too, but this is probably needed because selectors are not refcounted
+  // and can become stale.
+  if (CSSStyleSheet* geckoSheet = GetAsGecko()) {
+    geckoSheet->ClearRuleCascades();
+  }
 
   // let our containing style sets know that if we call
   // nsPresContext::EnsureSafeToHandOutCSSRules we will need to restyle the
diff --git a/layout/style/StyleSheet.h b/layout/style/StyleSheet.h
index 57a92a1d81b7..99ccd99fee1f 100644
--- a/layout/style/StyleSheet.h
+++ b/layout/style/StyleSheet.h
@@ -288,9 +288,6 @@ protected:
   // Traverse our inner, if needed, for cycle collection
   virtual void TraverseInner(nsCycleCollectionTraversalCallback &);
 
-  void ClearRuleCascades();
-  virtual void ClearRuleCascadesInternal() {}
-
   StyleSheet*           mParent;    // weak ref
 
   nsString              mTitle;